Field of the Invention
The present invention relates to a solid electrolytic capacitor in which an anode is Al foil including a core portion and a porous portion, and a cathode includes a solid electrolyte, and more particularly, a solid electrolytic capacitor which has great reliability.
Description of the Related Art
Solid electrolytic capacitors in which an anode is Al foil including a core portion and a porous portion, and a cathode includes a solid electrolyte are used for various electronic devices because the capacitors are long in product life, low in calorific value, and charged and discharged at high rates. Japanese Patent Application Laid-Open No. 2005-26257 proposes an example of such a solid electrolytic capacitor.
FIG. 10 is a cross-sectional view of a sold electrolytic capacitor 200 disclosed in Japanese Patent Application Laid-Open No. 2005-26257. The sold electrolytic capacitor 200 includes a plurality of capacitor elements CU each including an anode 201, a dielectric layer (not shown), and a cathode 202; Cu foil 204; an exterior member 206; and a first external electrode 207 and a second external electrode 208.
The anode 201 is Al foil including a core portion 201A and a porous portion 201B. At an end of the anode 201 closer to the first external electrode 207, a Zn layer 201C is formed, and a Ni layer 201D is formed on the surface of the Zn layer 201C. The dielectric layer is an Al oxide film formed on the surface of the porous portion 201B. The Zn layer 201C is formed by zinc substitution of a part of the Al oxide film formed on the surface of the porous portion 201B. The cathode 202 includes a solid electrolyte layer 202A formed on the Al oxide film surface, and a current collector layer 202B formed on the surface of the solid electrolyte layer 202A. Predetermined numbers of the capacitor elements CU are stacked on both front and back surfaces of the Cu foil 204. In FIG. 10, two capacitor elements CU are stacked on the front surface of the Cu foil 204, whereas two capacitor elements CU are stacked on the back surface thereof.
The capacitor elements CU adjacent to each other are attached to each other with a conductive adhesive 205. In addition, the Cu foil 204 and the capacitor element CU adjacent to the Cu foil 204 are attached to each other with the conductive adhesive 205. The exterior member 206 encloses therein the stacked capacitor elements CU and the Cu foil 204. The first external electrode 207 and the second external electrode 208 are formed on the surface of the exterior member 206. The first external electrode 207 connected to the anodes 201 includes a first Ni layer 207A and a second Ni layer 207B. The second external electrode 208 connected to the cathodes 202 with the Cu foil 204 interposed therebetween includes a first Ni layer 208A and a second Ni layer 208B.
In the solid electrolytic capacitor 200, the Zn layer 201C and the Ni layer 201D, at the end of each anode 201 exposed from the exterior member 206, are supposed to achieve high reliability with low impedance.